Performance of an ortho-para concentration measurement cryostat for hydrogen

In this paper the results of the performance tests of an ortho-para analyzer for hydrogen are presented. The measurement is based on the easy and reliable gauging of the adiabatic heat of conversion between the hydrogen allotropes. A hydrogen gas flow is brought to a defined temperature first by the means of a liquid nitrogen bath at 77 K. Subsequently it is led through a catalyst bed inside an adiabatic cell. The ortho-para ratio can be derived from a precise temperature measurement before and after the catalytic induced conversion. Vice versa, with a known para content of the hydrogen feed, the activity of a given catalyst sample can be determined. The discussion of the results of the performance tests includes a chapter for the essential proper preparation of the necessary ortho-para catalyst material and the use of a suitable database for the thermodynamic properties of orthohydrogen and parahydrogen. A slight drawback of this method is the relative large amount of hydrogen gas required compared to other ortho-para concentration measurements.